Low alloy, high hardness, temper resistant steel



United States Patent 3,128,175 LOW ALLOY, HIGH HARDNESS, TEMPERRESESTANT STEEL Alexander Nagy, Pittsburgh, Louis W. Lherbier, Cuddy,and Alexander Altieri, McDonald, Pa, assignors to Universal-CyclopsSteel Corporation, Bridgeville, Pa., a corporation of Pennsylvania NoDrawing. Filed July 15, 1960, Ser. No. 43,002 5 Claims. (Ci. 75-126) Thepresent invention relates to a novel alloy that is particularly usefulfor applications where high strength at elevated temperatures isrequired, as well as for the preparation of dies for use in the aluminumdie casting industry and for use in hot work forging die applications.

It is a major object of the present invention to provide alloy steelsespecially useful in aluminum die casting and hot work forging dieapplications, that have all the advantages of prior alloys for thoseapplications but are further advantageous in that they exhibit superiorresistance to tempering and heat checking.

Another object of the present invention is to provide dies for use inthe aluminum die casting industry as well as in hot work forging dieapplications, which are highly resistant to tempering and to heatchecking.

Still another object of the present invention is to provide improvedsteel for use in such applications as solid fuel rocket cases andstructural members of aircraft that are subject to aerodynamic heating.

The present invention is based on thediscovery that the advantageouscharacteristics of prior art die alloys can be provided in a steel alongwith a superior resistance to tempering and heat checking in acomposition consisting essentially, by weight, of about 0.25 to 0.50percent of carbon, up to 1 percent of manganese, 0.50 to 2 percent ofsilicon, 2 to 10 percent of chromium, 1.5 to 5 percent of molybdenum,0.25 to 2 percent of vanadium, 1 to 6 percent of cobalt and theremainder iron. Elements such as sulfur and phosphorus can be presenteither in normal amounts resulting from standard steel melting practicesor can be present in quantities sufficient to provide for freemachining. Lead and selenium can also be present to enhance freemachining characteristics where these are desirable. In addition, otheralloying constituents can be included in such amounts as desirable toattain a given characteristic as long as the advantages of thisinvention are not deleteriously affected. For example, nickel might beused in the alloy for specific property requirements.

Within the foregoing broad range, superior properties can be obtained ina composition containing, by weight, about 0.30 to 0.40 percent ofcarbon, 0.20 to 1 percent of manganese, 0.50 to 1.50 percent of silicon,3 to 4 percent of chromium, 2.5 to 3.5 percent of molybdenum, 0.50 to 1percent of vanadium, 1.50 to 2.50 percent of cobalt and the remainderiron. Here again sulfur and phosphorus can be present either in traceamounts or in amounts suflicient to provide for free machining, that isup to 0.50 percent. Lead and selenium may also be added if desirable forfree machining characteristics in amounts up to 0.25 percent.

The preferred range of compositions within the foregoing broad rangescontains, by weight, about 0.32 to 0.37 percent of carbon, 0.20 to 0.40percent of manganese, 0.80 to 1.20 percent of silicon, 3 to 3.5 percentof chromium, 2.60 to 2.90 percent of molybdenum, 0.65 to 0.85 percent ofvanadium, 1.50 to 2 percent of cobalt and the remainder iron andincidental impurities and alloying constituents which do notdeleteriously detract from the superior characteristics of the resultingcompositions. Within this preferred range exceptionally outstandingproperties of hardness and ultimate tensile strength at high temperatureare found.

The alloy steels of compositions within the invention are prepared inaccordance with standard mill practices. The material can be melted inany of the air electric arc melting furnaces, induction furnaces or byother means. Under certain circumstances the material can be meltedunder vacuum or in inert gas atmospheres. After melting, the moltenmetal is teemed into ingots. To obtain material from which dies may bemade, the ingots are hot worked by forging, pressing or rolling byinitially heating to a temperature of about 2000 F. The ingots areworked at this temperature until the desired reduction is obtained afterwhich they are cooled. The product may be in the form of square billets,round bars, die blocks, or some other form as may be required by thefinal die shape.

The die is then machined or prepared from the proper form of structure;thereafter it is heat treated by heating to temperatures of about 1800to 2000 F., held for the proper length of time depending on size andshape and then is quenched in air, oil, salt or other medium. Thistreatment is further followed by a tempering treatment at temperaturesup to about 1300 F. which involves heating to the tempering temperature,holding at that temperature for the proper period of time consistentwith size and shape and then air cooling. Under certain conditionssingle tempering treatments may be used, although the most satisfactoryresults for normal usage are obtained by using either a double or tripletempering treatment, that is the tempering cycle is repeated a number oftimes. It is possible also to precede the tempering treat ment by a deepfreezing treatment to temperatures as low as 320 F.

The invention will be further described by means of a specific examplein which the details are given by way of illustration and not by way oflimitation.

I An ingot was prepared by melting the various components in the usualmanner. Analysis of the ingot showed the following chemistry, in weightpercent:

C 0.34 Mn 0.29 Si 0.97 Cr 3.18 Mo 2.70 V 0.80 Co 1.73 Fe Bal.

The mechanical properties of the steel in the heat treated conditionwere determined. The data in all of the following tables were obtainedon specimens with the foregoing analysis. The steel specimens were airquenched from 1900" F. and then tempered at various temperatures in twocycles of three hours each. Hardness tests were made before and aftertempering. The hardness data obtained are:

From these data it is evident that the alloy of this invention evidenceshigh tempered hardness that stays surprisingly uniform and high throughthe temperature range Otf 800 to 1300 F. The alloy of the inventionfinds use at hardnesses of about 30 Rockwell C although it will be notedfrom the data in Table I that hardnesses of 40 Rockwell C are readilyobtained and that a minimum. of 50 Rockwell C is obtained at a temperingtemperature of 1100 F. This response to tempering is of primaryimportance in providing resistance to heat checking since it indicates ahigh tensile strength after exposure at elevated temperatures. It alsoshows that dies made therefrom will resist softening when used forextended periods of time at the indicated temperatures.

Thereafter, the room temperature tensile properties were determined onspecimens air quenched from 1900 F. and then tempered in two 3 hourcycles at the tempering temperature indicated in the followingtabulation:

1 Using a 1%" gauge length and 0.250 diameter.

The foregoing data demonstrate the high strengths that can be achievedin compositions Within the scope of this invention. It may be noted thatadequate ductility remained notwithstanding the high strength.Accordingly, it is evident that stock of the composition can be readilyformed to structural shapes for use in aircraft and similar applicationsas Well as be used as dies.

The elevated temperature tensile properties as well as the ruptureproperties of the steel were determined on specimens that were temperedusing a double cycle for 3 hours each at 1-100 F. after air quenchingfrom 1900 F. The tensile data are:

1 Using a 1% gauge length and 0.250 diameter.

As predicted from the tempered hardness data (Table 1), these data showthat the composition has high tensile strength at high temperatures.Accordingly, heat checking in dies made therefrom will be largelysuppressed. Moreover, these and sirnilar data show that our compositionscan consistently be prepared with an ultimate tensile strength of atleast 165,000 p.s.i. and :a yield strength of at least 150,000 p.s.i. attemperatures to 1100 F.

The rupture data obtained 'are;

1 Using a 1 gauge length and 0.160 diameter.

From the foregoing discussion and data, it is evident that the presentinvention provides compositions of outstanding usefulness Where highstrength at elevated temperatures are desired. Moreover, the uniformlyhigh hardness over a high temperature range indicates the resistance toheat checking that, in addition to the charcteristics of good toughness,good machinability and very good wear resistance, make these materialsof primary importance in the aluminum die casting industry and for usein hot Work forging die applications.

According to the provisions of the patent statutes, we have explainedthe principle of our invent-ion and have described what we now considerto represent its best embodiment. However, we desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A low alloy content, high hardness, temper resistant steel having acomposition consisting essentially, by Weight, of 0.30 to 0.40 percentof carbon, 0.20 to 1 percent of manganese, 0.50 to 1.50 percent ofsilicon, 3 to 4 percent of chromium, 2.5 to 3.5 percent of molydenum,0.50 to 1 percent of vanadium, 1.50 to 2.50 percent of cobalt and theremainder iron and incidental impurities that do not deleteriouslyaffect the product.

2. A low alloy content, high hardness, temper resistant steel having acomposition consisting essentially, by weight, of about 0.32 to 0.37percent of carbon, 0.20 to 0.40 percent of manganese, 0.80 to 1.20percent of silicon, 3 to 3.5 percent of chromium, 2.60 to 2.90 percentof molybdenum, 0.65 to 0.85 percent of vanadium, 1.50 to 2 percent ofcobalt and the remainder iron.

3. An allow in accordance with claim 2 containing at least one elementselected from the group consisting of sulfur, phosphorus, lead andselenium in an amount sufiicient to enhance the machiningcharacteristics thereof.

4. A steel in accordance with claim 1 characterized by a temperedRockwell C hardness of at least 50, with an ultimate tensile strength ofat least 165,000 p.s.i. and a yield strength of at least 150,000 p.s.i.,at temperatures up to at least 1100 F.

5. A die block composed of a steel in accordance with claim 4.

References Cited in the file of this patent UNITED STATES PATENTS2,462,665 Olcott Feb. 22, 1949 2,914,400 Roberts Nov. 24, 1959 FOREIGNPATENTS 560,228 Belgium Sept. 14, 1957 577,989 Canada June 16, 1959

1. A LOW ALLOY CONTENT, HIGH HARDNESS, TEMPER RESISTANT STEEL HAVING ACOMPOSITION CONSISTING ESSENTIALLY, BY WEIGHT, OF 0.30 TO 0.40 PERCENTOF CARBON, 0.20 TO 1 PERCENT OF MANGANESE, 0.50 TO 1.50 PERCENT OFSILICON, 3 TO 4 PERCENT OF CHROMIUM, 2.5 TO 3.5 PERCENT OF MOLYBDENUM,0.50 TO 1 PERCENT OF VANADIUM, 1.50 TO 2.50 PERCENT OF COBALT AND THEREMAINDER IRON AND INCIDENTAL IMPURITIES THAT DO NOT DELETERIOUSLYAFFECT THE PRODUCT.